1. Field of the Invention
The invention concerns an actuation device for clamping of workpieces, in particular, to a machine tool, for example, as by actuation of a chuck, there being an axially movable actuation member provided to actuate the chuck, and in which, moreover, the actuation device has an externally closed receiving space, which is filled with a volume-compressible pressurized medium, preferably silicone oil, and a movement of the actuation member is associated with a change in volume of the receiving space. Such an actuation device is known, for example, from the not previously published German Patent Application P 43 39 439. The content of this patent application is herewith included fully, including for purposes of incorporating features of this older application into claims of the present patent application.
2. Description of the Invention Background
Workholding apparatuses are used to support an object to be machined (a "workpiece") or a number of workpieces in precise orientations relative to a machine tool such as, for example, a milling machine. Such apparatuses may comprise vises that are attached to a table known as a "grid plate" that is attached or supported relative to the milling machine.
Single station vises and dual station vises are known in the art. Both of those types of workholders can be manually actuated or actuated by, for example, electric, hydraulic or pneumatic means. Manually operated vise-like workholders typically employ a fixed jaw and screw that has one or more movable clamping jaws operably attached thereto for movement relative to the fixed jaw. As the screw is rotated, the movable jaw(s) serve to clamp the workpiece(s) between the movable jaw(s) and the fixed jaw.
While such manually operated vises are well suited for supporting various types and numbers of workpieces, they are generally difficult to automate because a rotary force must be applied to the vise screw in a precise manner to ensure that proper clamping forces are repeatedly generated. Also, the magnitude of such clamping forces are dependent upon the operator either utilizing a torque wrench or similar tool to apply the requisite amount of torque or the vise is simply adjusted by "feel".
In an effort to address such problems associated with manually operated vises, hydraulically actuated vises have been developed. Such vises may also be of a single or dual station design and are generally operated by the application of hydraulic fluid under pressure to the vise. The clamping forces generated by such vises can be adjusted by varying the pressure of the hydraulic fluid which causes the jaws to clamp the workpiece(s). However, when power is accidentally lost to the hydraulic systems supplying the pressurized fluid to the vise, the jaws may be free to open which can result in the unintentional release of the workpiece(s) from the vise. Therefore, there is a need for a hydraulically actuated workholding vise that will remain in a clamped position when power is lost or discontinued.